IV-362 



The long-term type of toxicity is manifested through the gradual 

 destruction of the natural biota. The effects of sub-lethal con- 

 centrations of toxic materials are amplified through biological 

 magnification. Many animals, especially shellfish, can remove 

 these materials from the environment and store them in their tissues. 

 This magnification phenomenon has been documented with such pollu- 

 tants as pesticides, heavy metals, and radionuclides. The body 

 concentration of the toxicant may reach such a level that death 

 results in the host organism when the material is released to the 

 blood stream by physiological activity. Any higher carnivore con- 

 suming an organism with high tissue concentrations of toxic 

 materials may be subject to acute or fatal poisoning. Table IV. 5. 2 

 lists the biological magnification factors of five mollusks for 

 specific pesticides (IV-5-2). 



The pesticide group is of particular concern in the estuarine zone. 

 Estuaries are the terminus for most of the major river systems, 

 and as such they tend to concentrate the waterborne materials 

 carried in by the large terrestrial drainage systems. The biological 

 magnification capability of estuarine animals significantly increases 

 the hazard and destructive potential of any contributed pesticides. 

 Table IV. 5. 3 shows the concentration of selected pesticides that 

 will kill 50 percent of exposed shrimp within 48 hours. Shrimp are 

 one of the most sensitive groups of marine organisms (IV-5-1). 



